The proposed research is designed to examine the molecular and physiological events which accompany phenotypic expression in primary monolayer cultures of myogenic cells isolated from the chicken embryo. Studies are proposed on the complexity of the chicken genome as revealed by DNA reassociation analyses, satellite DNA isolation and in situ hybridization. A molecular hybridization analysis of myogenesis will be performed with purified DNA of various repetition frequencies and RNA isolated from prefusion and postfusion cells, and from BrdU inhibited cultures. The ability of BrdU inhibited cells to condition the culture medium will be investigated. Physiological studies will include examinations of the ability of stretched muscle fibers from myogenic cultures to respond to conditions which stimulate contraction and wave propagation in vitro.